The Antiterrorism and Effective Death Penalty Act (AEDPA) prohibits federal courts from hearing new evidence to support a claim that a petitioner’s state postconviction counsel negligently failed to develop the state court record, the U.S. Supreme Court held May 23 in Shinn v. Ramirez.
Sec. 2254(e)(2)(A) of AEDPA states that if a petitioner has “failed to develop the factual basis of a claim in State court proceedings,” a federal court “shall not hold an evidentiary hearing on the claim”, unless the petitioner satisfies one of two narrow exceptions.  
In 2012, the Court, in Martinez v. Ryan, adopted an equitable rule that ineffective assistance of postconviction counsel is “cause” to forgive procedurally defaulted ineffective-assistance-of-trial-counsel claims, in states which require petitioners to raise ineffective-trial-counsel claims for the first time during state postconviction proceedings.
In 2013, the Court, in Trevino v. Thaler, extended this rule to states where the judicial system effectively forecloses direct review of trial-ineffective-assistance claims.
The question in Ramirez was “whether the equitable rule announced in Martinez permits a federal court to dispense with Sec. 2254(e)(2)’s narrow limits because a [petitioner’s] state postconviction counsel negligently failed to develop the state court record,” the Court said.  “We conclude that it does not.”
David Martinez Ramirez was convicted of murder, and sentenced to death.  The Arizona Supreme Court affirmed on direct appeal.
Ramirez then filed a state postconviction petition, which raised various claims, but not the one later raised in federal court – that his trial counsel was ineffective in not conducting a complete mitigation investigation.
After losing in state postconviction, Ramirez sought federal habeas relief.  
Ramirez claimed his failure to develop his mitigation claim in state court should be excused because his state postconviction counsel was himself ineffective in failing to raise the claim and present facts to support it.
The District Court allowed Ramirez to present evidence to support his request to excuse the defaulted claim.  The District Court then ruled the default was excused, but denied the ineffective assistance of trial counsel claim on the merits.
The Ninth Circuit similarly held that Ramirez’s failure to raise and develop the trial-ineffective-assistance-claim was excused, but declined to decide the merits.  Instead, the Ninth Circuit remanded to allow further evidentiary development to litigate the merits.  
The Supreme Court, in a 6-3 opinion, reversed, and held that AEDPA does not permit a federal court to allow evidentiary development of a defaulted claim “simply because” postconviction counsel is alleged to have negligently failed to develop the state court record.
Habeas relief is “narrowly circumscribed” in order to “respect our system of dual sovereignty,” the Court said.  “[O]nly rarely may a federal habeas court hear a claim or consider evidence that a prisoner did not previously present to the state courts in compliance with state procedural rules.”
“To ensure that federal habeas corpus retains its narrow role, AEDA imposes several limits on habeas relief, and we have prescribed several more,” the Court said.
Sec. 2254(e)(2) of AEDPA provides that if a prisoner “has failed to develop the factual basis of a claim in State court proceedings,” a federal court may not hold “an evidentiary hearing on the claim” except in two limited circumstances, the Court said.
One is where a new and previously unavailable rule of constitutional law has been announced by the Supreme Court and applied retroactively.  The other is for a “factual predicate that could not have been previously discovered through the exercise of due diligence.”  
Even if a petitioner satisfies one of these two contingencies, AEDPA still requires him to show by clear and convincing evidence that no reasonable fact-finder would have convicted him, the Court said.
But “even if all of these requirements are satisfied, a federal habeas court still is not required to hold a hearing or take any evidence,” the Court said.  “Like the decision to grant habeas relief itself, the decision to permit new evidence must be informed by principles of comity and finality that govern every federal habeas case.”
A state postconviction petitioner bears responsibility for all attorney errors during those proceedings, the Court said.
“[U]nder Sec. 2254(e)(2), a [petitioner] is ‘at fault’ even when a state postconviction counsel is negligent,” the Court said.  “In such a case, a federal court may order an evidentiary hearing or otherwise expand the state-court record only if the [petitioner] can satisfy Sec. 2254(e)(2)’s stringent requirements.”
“Sec. 2254(e)(2) is a statute we have no authority to amend,” the Court said.  “Where Congress has erected a valid barrier to habeas relief, a court cannot decline to give it effect.”
Martinez had said its holding “ought not put a significant strain on state resources” because a State faced with the question of whether to excuse a procedural default “may answer that the defaulted claim is wholly without factual support,” the Court said.  “That assurance has bite only if the State can rely on the state court record.”
“We now hold that, under Sec. 2254(e)(2), a federal habeas court may not conduct an evidentiary hearing or otherwise consider evidence beyond the state-court record based on ineffective assistance of state postconviction counsel,” the Court ruled.
Dissenting opinion
Justice Sotomayor dissented, joined by Justices Kagan and Breyer.
Sotomayor said the Court “all but overruled” Martinez and Trevino.
“This decision is perverse.  It is illogical,” she said.  “It makes no sense to excuse a habeas petitioner’s counsel’s failure to raise a claim altogether because of ineffective assistance in postconviction proceedings, as Martinez and Trevino did, but to fault the same petitioner for that postconviction counsel’s failure to develop evidence in support of the trial-ineffectiveness claim.”
“Martinez repeatedly recognized that to prove a trial-ineffectiveness claim … habeas petitioners frequently must introduce evidence outside of the trial record,” Sotomayor said.  “Ineffective-assistance claims frequently turn on errors of omission: evidence that was not obtained”.  
“To hold a petitioner at fault for not developing a factual basis because of postconviction counsel’s ineffectiveness in the Martinez context” is “to eliminate altogether such evidentiary development and doom many meritorious trial-ineffectiveness claims that satisfy Martinez,” Sotomayor said.
“[T]he Court limits Martinez and Trevino to their facts, emptying them of all meaning in the ordinary case (where, as those precedents explain, a trial-ineffectiveness claim will necessarily rely on evidence beyond the trial record)”, she said.